1. Field of the Invention
The present invention relates to a pattern formation member applied to a sectioning image observation apparatus for observing/measuring sample microstructure or three-dimensional shape of a sample by using light and a sectioning image observation apparatus using them.
2. Description of the Related Art
Conventionally, as a sectioning image observation apparatus, a confocal microscope using a rotation disk called Nipkow rotation disk where a number of pin holes are arranged in spiral with an interval of about ten times of the pin hole diameter is known.
FIG. 1 shows the schematic configuration of a confocal microscope using such a Nipkow rotation disk, wherein a condenser lens 2 and a PBS (polarized beam splitter) 3 are arranged on a light path of the light emitted from a light source 1 such as halogen light source or mercury light source or others, and a Nipkow rotation disk (called rotation disk, hereinafter) 4, a first imaging lens 5, ¼ wavelength plate 6 and a sample 8 through an objective 7 are arranged on the reflected light path of the PBS 3. In addition, a CCD camera 10 is arranged through a second imaging lens 9 on the filtered light path of the PBS 3 of the light reflected from the sample 8. A monitor 11 is connected to the image output terminal of this CCD camera 10 for displaying the image taken by the CCD camera.
Here, pin holes 4a are arranged in spiral on the rotation disk 4 with an interval of about ten times of the pin hole diameter between respective pin holes, and the rotation disk 4a is connected to the shaft of a not shown motor via a rotation shaft 12 and rotated at a fixed rotation speed.
In such configuration, the light emitted from the light source 1 passes through the condenser lens 2 and only polarized component of a fixed direction is reflected by the PBS 3 and input to the rotation disk 4 rotating at the fixed speed, and the light filtered by the pin hole 4a of this rotation disk 4 passes through the first imaging lens 5, circularly polarized by the ¼ wavelength plate 6, imaged by the objective lens 7 and input to the sample 8. On the other hand, the light reflected from the sample 8 passes through the objective lens 7, takes a polarization direction orthogonal to the incident light again at the ¼ wavelength plate 6, and projects the sample image on the rotation disk 4 by means of the first imaging lens 5. A focused portion of the sample image projected on the rotation disk 4 passes through the pin hole 4a, further passes through the PBS 3 and taken by the CCD camera 10 through the second imaging lens 9. A confocal image taken by the CCD camera 10 is displayed on the monitor 11.
Such confocal microscope allows to observe a so-called sectioning image, namely image for each level of the sample 8, by moving the focus vertically (Z axis direction), as only images having focused position (height) where the pin hole 4a of the rotation disk 4 passes can be observed.
By the way, for the confocal microscope using such Nipkow rotation disk, it is necessary to dispose pin holes on the rotation disk so that unevenness may not come into prominence in the observation field during the eye observation or imaging by a CCD camera. In short, it is necessary to arrange pin holes so that the sample observation field is illuminated evenly within a human perceptible time interval (about 1/20 to 1/30 sec) or CCD camera exposure time (often 1/60 or 1/30 sec).
Therefore, conventionally, various proposals have been made concerning the pin hole arrangement and, for instance, an arrangement wherein a plurality of pin holes are arranged in spiral in the rotation disk radial direction with an equal angle is known as the simplest arrangement. However, in such pin hole arrangement, the brightness of captured image is uneven, because the pin hole pitch is different in the outer circumferential section and the inner circumferential section of the rotation disk.
As a method to solve such problem, various pin hole arrangements for reducing the uneven brightness of captured image, such as an arrangement wherein the radial pitch of the locus of the virtual center line connecting centers of a plurality of pin holes composing pin hole lines arranged in spiral and the circumferential pitch along the spiral are made equal, or an arrangement wherein all pin holes composing a plurality of pin hole lines are differentiated in diameter at their center position have been proposed.
However, in the former pin hole arrangement, certainly, the image brightness in the observation field is even when the rotation disk center and the rotation axis agree exactly, but the observed image brightness is uneven when the rotation disk center and the rotation axis disagree. In general, the pin hole diameter is so small as about several dozens of μm (45 μm for 100 times, 100 μm for 250 times); therefore, it is necessary to limit the difference between the rotation disk center and the rotation center to 10 μm or less, namely sufficiently smaller than the pin hole diameter so that the observed image brightness may not be uneven, thereby, requiring an extremely high precision for perforation of pin hole on the rotation disk, shaping of the rotation disk, attachment of the rotation disk to the rotation shaft, or other processing.
On the other hand, the latter pin hole arrangement is improved to reduce the unevenness of observed image brightness; however, the unevenness is certainly reduced, but not eliminated.
In addition, when pin holes are formed on the rotation disk in this way, the pin hole arrangement is so devised not to make the observed image brightness uneven for all samples, and the pin hole is positioned using a complicated pattern prepared extremely precisely, in order to position each pin hole exactly. For instance, for Nipkow rotation disk, Cr or low-reflective Cr film is formed on a glass substrate, masked with a pin hole pattern and etched, and this mask is prepared by a EB drawing machine using electron beam similarly as semiconductor manufacturing, making the rotation disk preparation very costly and expensive due to the use of such complicated pattern mask.
Therefore, in order to solve these problems, it has been proposed a rotation disk wherein a straight line pattern section 141 including linearly formed translucent sections and shield sections arranged alternately, a full translucent section 142, and shield sections 143, 144 in each fan-shaped areas between these straight line pattern section 141 and full translucent section 142 are disposed on a rotation disk 14 as shown in FIG. 3A, and the width of translucent sections and shield sections of the straight line pattern section 141 among them is set to about several dozens of μm similarly as the pin hole diameter, and formed to 1:1 as shown in FIG. 3A and FIG. 3B.
According to such rotation disk, first, an observation when the observation field passes through the straight line pattern section 141 is taken by the CCD camera, then an observation when it passes through the full translucent section 142 is taken by the CCD camera. In this case, a combined image (confocal image including non-confocal component) including not only an image having focused position (height) components (confocal component), but also image having non-focused position (height) components (permeated non-confocal component) is obtained, because the ratio of each width of translucent sections 141a and shield sections 141b is equal, for the image taken in the straight line pattern section 141. Consequently, only the confocal image having position (height) components in good focus ban be obtained by the difference calculation of bright-field taken through the full translucent section 142 from this combined image. In addition, uneven brightness is not generated in the observation image even when the rotation disk rotation center has shifted, and the rotation disk preparation cost will be limited because the pattern for creating the straight line pattern section 141 including linearly formed translucent sections and shield sections arranged alternately is a simple linearly pattern.
On the contrary, in the rotation disk 141 shown in FIG. 3A and FIG. 3B, the non-confocal component is prominent, because the ratio of each width of translucent sections and shield sections of the straight line pattern section 141 is 1:1. Therefore, a so-called sectioning effect, containing only confocal image can be expected only by the difference calculation. This generates problems such as impossibility of directly viewing the confocal image, necessity of operation equipment such as computer for image processing, enlargement of equipment scale, cost increase, and moreover, two images subjected to the difference calculation are susceptible to disturbance such as vibration, because they are taken with different timing.